In order to improve the recording capacity of a hard disk drive (hereafter referred to as an HDD), the track density must be increased by reducing the magnetic pole width at the magnetic writer head and, at the same time, the recording capability must be improved by utilizing a material having a high saturation magnetization. When a perpendicular magnetic recording method is adopted, a high coercivity must be assured in the medium in order to improve the recording resolution. In addition, in order to assure the desired overwrite characteristics in the writer head, the writer magnetic pole must be constituted by using a material with a high saturation magnetization such as an FeCo-system material, a CoNiFe ternary alloy film, FeC or FeN.
However, while the use of the type of material described above to constitute the magnetic pole improves the recording capability, it leads to a problem of so-called pole erase at a perpendicular magnetic writer head whereby a signal having been recorded by a writer magnetic pole becomes erased when a write operation is not executed.
A soft magnetic film at the perpendicular magnetic writer head imparts a magnetic flux with its magnetic anisotropy directed along the transverse direction to the head by assuming a magnetizing rotation mode. Namely, the residual magnetization manifesting toward the medium is minimized so as to avoid the generation of an excess residual magnetic flux when the magnetic writer head is not engaged in a write operation.
However, since the front end of the writer magnetic pole width comes to narrow, shape form anisotropy is induced which destabilizes the structure of the magnetic domain. This instability in the magnetic domain structure is thought to be the root cause of the pole erase phenomena, since it induces trapping at the magnetic wall, which keeps the direction of the magnetization unchanged toward the medium even after the write operation ends, allowing the magnetic flux to leak into the medium, and it makes erasing the recorded data on the medium.
A soft magnetic multilayer film achieved by laminating different types of magnetic films or magnetic films and nonmagnetic films over several layers to several tens of layers is used as a means for stabilizing the magnetic domain structure in the related art. In addition, while there is a longitudinal writer head in the related art adopting a structure having a hard, thin magnetic film arranged over the shield area, the distance to the soft magnetic film is considerable and thus, this structure is not effective enough to prevent pole erase at the perpendicular writer head.
To summarize, the problem of pole erase occurring when a perpendicular magnetic recording method is used cannot be completely eliminated simply by stabilizing the magnetic domain structure of the soft magnetic film because of the magnetic field generated from the perpendicular medium.
Furthermore, if the magnetic pole width is further reduced to keep pace with the ever increasing need to improve recording density, the shape form anisotropy will become even more dominant to allow a significant extent of residual magnetization at the magnetic pole tip toward the medium surface, which is bound to exacerbate the problem.